1. Field of the Invention
This invention relates to the field of security systems for motor vehicles such as automobiles and aircraft, and, more specifically, to intrusion detection using pyroelectric detectors.
2. Related Background Art
Automotive theft is a serious problem in the United States and in many other countries. Many security devices, including car alarms, ultrasonic scanners, ignition sensors, central locking systems, hands-free cellular phones, kill switches, electronic or RF keys, steering wheel locking and vehicle tracking devices are available to address this problem.
These devices can be categorized as either original equipment manufacturer (OEM) systems, which are built into the automobile by the manufacturer, or after-market systems, which are added to the automobile subsequent to manufacture. In general, OEM systems are superior to after-market systems because they can be incorporated in an OEM supplied component to reduce or eliminate additional installation costs in the vehicle assembly plant. In contrast, after-market systems can be expensive, bulky and difficult to install. Existing OEM systems, however, are typically included only on high priced luxury cars. While OEM security devices are sometimes available as an option on less expensive vehicles, optional systems may have higher installation costs. An OEM security device that is inexpensive enough to include as standard equipment would be preferable.
Various types of OEM security devices are commercially available. One such device is an ultra-sound intrusion detection system described in U.S. Pat. No. 5,424,711. In this system, ultrasound emission and reception elements are provided as a plurality of separate elements located at or near the internal surface of the roof of the vehicle. More specifically, the elements are located in the region of the pillars between the front and the rear side panes.
The Clifford Electronics and Hornet auto security systems are two examples of commercially available after-market security systems. The Clifford systems, including the SuperNova II, the Arrow II and the Concept series, are radar based and are usually installed with the radar module located under the floor carpet in the center part of the vehicle. This system is available from Clifford Electronics, 20750 Lassen St., Chatsworth, Calif. 91311. The Hornet auto-security systems, ProSeries model, detects open vehicle doors and is electrically tied to the door circuitry. The system is available from Hornet Directed Electronics Inc., 2560 Progress St., Vista, Calif. 92083.
The above OEM and after-market systems, however, suffer from a number of significant drawbacks. In particular, due to their active nature, they require a relatively large amount of power. Due to the relatively large package size, the mounting of the devices in the pillars, under the floor carpet in the interior of the car, or in the doors is challenging. In some constructions, replacement in the event of malfunction is difficult. The body structure and the trim of the vehicle must also be designed to adequately accommodate these parts. In the Clifford systems, the radar may not function properly when certain metalized window tints are present. Finally, in the above described Hornet system, additional sensors and mechanisms are required to detect intrusion into the vehicle via other paths (i.e. open or broken windows), and water in the door may cause a malfunction due to the mechanical nature of the switches.
Intrusion detection systems may also be used in aircraft, which are often equipped with expensive equipment and systems. Currently available aircraft intrusion detection systems, however, are either too expensive or require a large installation space which is not available in many types of aircraft. For example, U.S. Pat. Nos. 4,933,668 and 5,063,371 describe aircraft security systems that include a central control unit with several remotely placed controllers and numerous sensors. These systems, however, tend to be bulky, heavy, complicated, and expensive. They consume large amounts of power, which may require the use of extra batteries or power supplies in the aircraft. This can increase the bulk and weight further still. In addition, installation of these systems can be very complicated and time consuming. U.S. Pat. No. 4,797,657 describes another type of portable detection system for use inside aircraft with delayed arming and activation but no remote access.
Until now, no intrusion detection systems have been available for use on-board aircraft that have sufficiently low power consumption, low weight, and do not require dedicated batteries. Similar considerations also apply for boats, busses, trucks, trains, and other uses.
One desirable attribute for intrusion detection systems for vehicles is low power consumption during operation. This allows the device to operate for extended periods of time while the vehicle is not being used without draining the battery. This is particularly important with cars and aircraft, which may sit unused for weeks or even months at a time. Thermal energy detection requires very little energy in comparison with active infrared and ultrasonic devices. Thus, the sensing of thermal energy is preferred over other means of detection. Thermal energy can be detected with a variety of devices such as thermistors, thermopiles, bolometers, and photon detectors. However, these thermal energy detectors do not have sufficient sensitivity in the detection of thermal fluctuations. Furthermore, photon detectors (i.e. HgCdTe detectors) must be cooled down to liquid nitrogen temperature (negative 195.degree. C.) and thus are impracticable for use in vehicle intrusion detection systems.
Pyroelectric intrusion detection systems have been used as motion sensors inside buildings for security and intrusion detection purposes. Pyroelectric systems are passive in nature, and they detect the presence of an intruder in a defined area by sensing and responding to the thermal radiation of the intruder. However, pyroelectric intrusion detecting devices for buildings tend to be expensive, bulky and require a lot of power (e.g., several Watts). This makes them unsuitable for use in vehicles, where any intrusion system must be relatively inexpensive, compact, consume very low power, yet be reliable. Furthermore, building intrusion detection systems may not operate properly in a vehicle because of the extreme temperatures that can occur inside the vehicle.
Pyroelectric detectors have also been used inside automobiles for applications other than intrusion detection. U.S. Pat. Nos. 5,071,160 and 5,482,314 are directed to infrared systems for use with air bag deployment or other types of safety restraint systems for protection of passengers in the event of a collision. These systems are designed to sense the presence, position and type of object in a seat, and provide a condition signal to the safety restraint system, such as an air bag. These systems can detect the presence and orientation of a child seat (front or rear-facing), an out-of-position occupant or other types of occupancy, and determine the appropriateness of deploying an air bag, thereby increasing the reliability and safety of an air bag activation system. More specifically, an ultrasonic acoustic sensor senses the position of the driver, a pyroelectric sensor senses the presence of the driver, a pressure transducer within the seat senses the approximate weight of the driver and an air bag control module triggers deployment of the air bag.
U.S. Pat. No. 5,585,625 describes yet another arrangement for detecting the presence, position, and type of object in a seat in vehicles. This system operates by illuminating the seat with infrared radiation and detecting an image of the seat using received radiation.
Each of these pyroelectric detector systems, however, are only used when the ignition of the vehicle is on. Moreover, none of these systems use a pyroelectric detector to detect intrusion into a vehicle. Prior pyroelectric detection systems were not suitable for use as intrusion detection systems in vehicles because they would consume too much power, and because they would be prone to false alarms in vehicular environments. In addition, none of the prior systems offer a low-power intrusion detection system for use in vehicles which can be easily integrated with other components of the vehicle.